The present invention relates to a communication apparatus that employs a multi-carrier modulation/demodulation system. The invention particularly relates to a communication apparatus and a communication method capable of realizing data communications by using existing communication lines, based on a DMT (Discrete Multi Tone) modulation/demodulation system or an OFDM (Orthogonal Frequency Division Multiplex) modulation/demodulation system. However, the present invention is not limited to a communication apparatus that carries out data communications based on the DMT modulation/demodulation system. It is also possible to apply the present invention to all communication apparatuses that carry out wire communications and radio communications based on a multi-carrier modulation/demodulation system and a single-carrier modulation/demodulation system via normal communication lines.
The operation of a conventional communication apparatus will be explained below. First, the operation of a transmission system of a conventional communication apparatus that employs the OFDM modulation/demodulation system as a multi-carrier modulation/demodulation system will be briefly explained. When data communications are carried out according to the OFDM modulation/demodulation system, the transmission system carries out a tone ordering processing. In other words, the transmission system allocates transmission data of a transmittable number of bits to a plurality of tones (multi-carriers) of a frequency band that has been set in advance. For example, transmission data of a predetermined number of bits is allocated to tone 0 to tone X (X is an integer that shows a number of tones) of each frequency. The transmission data is multiplexed for each one frame by carrying out the tone ordering processing and an encoding processing.
Further, the transmission system carries out an inverse fast Fourier transform (IFFT) to multiplexed transmission data, and converts a parallel data after the inverse fast Fourier transform into a serial data. Then, the transmission system converts a digital waveform into an analog waveform with a D/A converter. Last, the transmission system applies a low-pass filter, and transmits the transmission data to a transmission route.
Next, the operation of a reception system of the conventional communication apparatus that employs the OFDM modulation/demodulation system as a multi-carrier modulation/demodulation system will be briefly explained. When data communications are carried out according to the OFDM modulation/demodulation system, the reception system applies a low-pass filter to a received data (the above transmission data). Then, the reception system converts an analog waveform into a digital waveform with an A/D converter, and carries out an adaptive equalization of a time domain with a time domain equalizer.
Further, the reception system converts the serial data after the adaptive equalization of the time domain into a parallel data. The reception system carries out a fast Fourier transform to this parallel data, and then carries out an adaptive equalization of a frequency domain with a frequency domain equalizer.
The data after the adaptive equalization of the frequency domain is converted into a serial data according to a composite processing (a maximum likelihood composite method) and a tone ordering processing. Then, a rate converting processing, an FEC (forward error correction), a descramble processing, and a CRC (cyclic redundancy check) are carried out. Last, a transmission data is reproduced.
As explained above, the conventional communication apparatus that employs the OFDM modulation/demodulation system makes it possible to carry out communications at a high transmission rate by utilizing good transmission efficiency and flexibility of functions that cannot be obtained according to the CDMA and the single-carrier modulation/demodulation system.
However, the conventional communication apparatus that employs the OFDM modulation/demodulation system has had room for improvement in the transmission system and the reception system from the viewpoint of xe2x80x9cfurther improvement in the transmission ratexe2x80x9d. There has been a problem that the conventional communication apparatus has not realized an optimum transmission rate by making a maximum utilization of the xe2x80x9cgood transmission efficiencyxe2x80x9d and the xe2x80x9cflexibility of functionsxe2x80x9d that are the characteristics of the OFDM modulation/demodulation system.
Therefore, it is an object of the present invention to provide a communication apparatus and a communication method capable of realizing further improvement in the transmission rate, by realizing half symbolization in the multi-carrier modulation/demodulation system.
The communication apparatus according to the present invention is a structure that employs the multi-carrier modulation/demodulation system, further comprises a transmission unit which generates a transmission symbol by carrying out an inverse Fourier transform to a signal after a BPSK modulation and transmits the transmission symbol in a half-symbolized status, and a reception unit which carries out a predetermined Fourier transform to the half-symbolized received symbol in order to extract even sub-carriers to demodulate data allocated to the sub-carriers, carries out an inverse Fourier transform to the data allocated to the even sub-carriers to generate a first symbol that is structured with a time waveform of even sub-carriers, removes the first symbol component from the received symbol to generate a second symbol that is structured with a time waveform of odd sub-carriers, adds a symbol obtained by copying and inverting the symbol to the back of the second symbol to generate a third symbol, and carries out a predetermined Fourier transform to the third symbol in order to extract odd sub-carriers to demodulate data allocated to the sub-carriers.
In a communication apparatus according to the next invention, the reception unit further carries out an inverse Fourier transform to the data allocated to the odd sub-carriers to generate a fourth symbol that is structured with a time waveform of odd sub-carriers, thereafter, removes the fourth symbol component from the received symbol, and then carries out demodulation processing by using a received symbol after the removal of the fourth symbol component.
A communication apparatus according to the next invention is a structure that employs a multi-carrier modulation/demodulation system, further comprises a transmission unit which generates a transmission symbol by carrying out an inverse Fourier transform to a signal after a BPSK modulation and transmits the transmission symbol in a half-symbolized status, and a reception unit which generates a first symbol that is structured with time axis data of even sub-carriers and odd sub-carriers by generating all data combinations that could occur and by sequentially carrying out an inverse Fourier transform to the data combinations, generates a second symbol that is half-symbolized by deleting a latter half section of the first symbol and subtracts an occasionally-generated second symbol from the received symbol, calculates a squared average (a dispersion value) of amplitude by using a received subtraction result and detects a minimum value from the squared average, and determines a data combination corresponding to the minimum value as most likely from among all the data combinations that could occur and decides this data combination as a final decision value.
A communication apparatus according to the next invention is a structure that employs a multi-carrier modulation/demodulation system, further comprises a transmission unit which generates a transmission symbol by carrying out an inverse Fourier transform to a signal after a BPSK modulation and transmits the transmission symbol in a half-symbolized status, and a reception unit which generates a first symbol that has the same length as that of the symbol before the half-symbolization by adding a symbol of all 0 to the back of a half-symbolized received symbol, extracts even sub-carriers and odd sub-carriers by carrying out a Fourier transform to the first symbol, and judges individually data that is allocated to the even sub-carriers and data that is allocated to the odd sub-carriers.
A communication apparatus according to the next invention is a structure that employs a multi-carrier modulation/demodulation system, and further comprises a reception unit which generates a transmission symbol by carrying out an inverse Fourier transform to a signal after a QPSK modulation and transmits the transmission symbol in a half-symbolized status, and a transmission unit which generates a first symbol that has the same length as that of the symbol before the half-symbolization by adding a symbol of all 0 to the back of a half-symbolized received symbol, extracts even sub-carriers and odd sub-carriers by carrying out a Fourier transform to the first symbol, makes a hard decision on data of the even sub-carriers, calculates a component that becomes an interference to the odd sub-carriers from the decision result, removes the interference component from the odd sub-carriers after the extraction, makes a hard decision on data of odd sub-carriers after the removal of the interference component, calculates a component that becomes an interference to the even sub-carriers from the decision result, and removes the interference component from the even sub-carriers after the extraction, thereafter, repeatedly executes the interference component removal processing by a predetermined number of times, and outputs decision results of both sub-carriers as final decision values.
A communication method according to the next invention comprises a transmission step of generating a transmission symbol by carrying out an inverse Fourier transform to a signal after a BPSK modulation and transmitting the transmission symbol in a half-symbolized status, an even sub-carrier demodulating step of carrying out a predetermined Fourier transform to the half-symbolized received symbol in order to extract even sub-carriers and demodulating data allocated to the sub-carriers, a first-symbol generating step of generating a first symbol that is structured with a time waveform of even sub-carriers by carrying out an inverse Fourier transform to the data allocated to the even sub-carriers, a second-symbol generating step of generating a second symbol that is structured with a time waveform of odd sub-carriers by removing the first symbol component from the received symbol, a third-symbol generating step of generating a third symbol by adding a symbol obtained by copying and inverting the symbol to the back of the second symbol, and an odd sub-carrier demodulating step of carrying out a predetermined Fourier transform to the third symbol in order to extract odd sub-carriers and demodulating data allocated to the sub-carriers.
A communication method according to the next invention further comprises a fourth-symbol generating step of generating a fourth symbol that is structured with a time waveform of odd sub-carriers by carrying out an inverse Fourier transform to the data allocated to the odd sub-carriers, and a removing step of removing the fourth symbol component from the received symbol, and the communication method thereafter carries out a demodulation processing by using a received symbol after the removal of the fourth symbol component.
A communication method according to the next invention comprises a transmission step of generating a transmission symbol by carrying out an inverse Fourier transform to a signal after a BPSK modulation and transmitting the transmission symbol in a half-symbolized status, a first-symbol generating step of generating a first symbol that is structured with time axis data of even sub-carriers and odd sub-carriers by generating all data combinations that could occur and by sequentially carrying out an inverse Fourier transform to the data combinations, a second-symbol generating step of generating a second symbol that is half-symbolized by deleting a latter half section of the first symbol, a subtracting step of subtracting an occasionally-generated second symbol from the received symbol, a squared-average calculating step of calculating a squared average (a dispersion value) of amplitude by using a received subtraction result, a minimum-value detecting step of detecting a minimum value from the squared average, and a decision step of judging a data combination corresponding to the minimum value as most likely from among all the data combinations that could occur and deciding this data combination as a final decision value.
A communication method according to the next invention comprises a transmission step of generating a transmission symbol by carrying out an inverse Fourier transform to a signal after a BPSK modulation and transmitting the transmission symbol in a half-symbolized status, a first-symbol generating step of generating a first symbol that has the same length as that of the symbol before the half-symbolization by adding a symbol of all 0 to the back of a half-symbolized received symbol, a sub-carrier extracting step of extracting even sub-carriers and odd sub-carriers by carrying out a Fourier transform to the first symbol, and a decision step of judging individually data that is allocated to the even sub-carriers and data that is allocated to the odd sub-carriers.
A communication method according to the next invention comprises a transmission step of generating a transmission symbol by carrying out an inverse Fourier transform to a signal after a QPSK modulation and transmitting the transmission symbol in a half-symbolized status, a first-symbol generating step of generating a first symbol that has the same length as that of the symbol before the half-symbolization by adding a symbol of all 0 to the back of a half-symbolized received symbol, a sub-carrier extracting step of extracting even sub-carriers and odd sub-carriers by carrying out a Fourier transform to the first symbol, a first interference component calculating step of making a hard decision on data of the even sub-carriers and calculating a component that becomes an interference to the odd sub-carriers from the decision result, a first removing step of removing the interference component from the odd sub-carriers after the extraction, a second interference component calculating step of making a hard decision on data of odd sub-carriers after the removal of the interference component and calculating a component that becomes an interference to the even sub-carriers from the decision result, and a second removing step of removing the interference component from the even sub-carriers after the extraction, thereafter, the communication method executes the interference component removal processing by a predetermined number of times, and outputs decision results of both sub-carriers as final decision values.